1. Field of the Invention
The present invention relates to a rotation preventing mechanism used to support a driving mechanism such as a scroll compressor and the like. More particularly, the present invention relates to a ball coupling as a rotation preventing mechanism for improving the assembling properties thereof when it is mounted on a structural member.
2. Description of the Related Art
Conventionally, scroll type compressors include a pair of scroll members which confront each other and execute a turning motion in which the rotation of one of the scroll members about its own axis is prevented with respect to the other. One of the pair of scroll members is a stationary swirl member fixed to a housing or the like and the other is a movable swirl member driven by a driving mechanism while its rotation on its own axis is prevented by a rotation preventing mechanism.
The rotation preventing mechanism of the conventional scroll type compressors is disposed on the side (back surface) of the movable swirl member which is opposite to the side thereof confronting the stationary swirl member in order to prevent the rotation of the movable swirl member on its axis. The movable swirl member executes a relative circular motion in confrontation with the stationary swirl member.
The conventional rotation preventing mechanism is composed of a ball coupling, and a pair of rings and a pair of thrust races are formed as separate members. The pair of rings accommodate thrust balls 71 therebetween and the thrust races are disposed outside the rings. One of the rings to fixed to the inner wall of a front housing by a pin together with one of the thrust races, whereas the other of the rings is fixed to the back surface of the movable scroll member by a pin together with the other of the thrust races.
However, the thrust races as the components of the ball coupling of the conventional scroll type compressor have a drawback that they are gradually deformed because they are subjected to the thrust load of the movable scroll member through the thrust balls when the compressor is operated.
Each of the thrust races according to prior art is composed of an annular steel sheet member having a rectangular cross section. Conventionally, the thrust race is subjected to heat treatment to increase the strength thereof. However, the inside of the race sheet member of the thrust race remains as a residual austenite phase as it is, while the surface phase of the race sheet member is transformed to martensite.
Therefore, the scroll type compressor has a drawback that when it is operated, the volume of the austenite phase remaining at the central portion of the thrust race is expanded when the austenite phase is transformed to the martensite phase, whereby the thrust race is deformed.